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### Can Variables Be Capital Letters?

```Date: 09/19/2006 at 10:32:15
From: Annie
Subject: Naming variables

I have a friend who was marked down for using capital letters for
variables--3A.  The teacher said it must be a lower case letter--3a.
is, is it a rule or is it what people usually do?

```

```
Date: 09/19/2006 at 12:28:44
From: Doctor Peterson
Subject: Re: Naming variables

Hi, Annie.

There is no rule that you can't use a capital letter as a variable; it
is done all the time, though certainly less often than lower case.
For example, the area of a trapezoid is sometimes written as

A = (B + b)h/2

where A is the area, B is one base and b is the other, and h is the
height.

There IS a rule, however, that once a variable is defined, you should
not change the case.  Often students prefer writing capital letters,
and will change a variable r in a problem to R in their answer.  This
should be discouraged, as you can see from my example above: B and b
are different things, and if you habitually write b as B, you will

I would never mark an answer wrong if the student chose a capital
letter for himself; I might call it wrong if he changed the case of a
variable that was given in a problem, especially if there were mixed
cases given.

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
http://mathforum.org/dr.math/

```

```
Date: 09/23/2006 at 00:40:14
From: Annie
Subject: Thank you (Naming variables)

Thanks so much for the help.  You answered my question completely and
I really appreciate your quick response.  It is great to know I can
get my questions answered when I have them.  Thanks again!  Annie
```
Associated Topics:
Middle School Algebra

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